LED signal problem....

[tramcar trev]

As those of you following my progress will recall I made up some bi colour led signals. Sooooooooo being one to want things to work I tested the leds at every stage of manufacture and once satified I encapsulated a batch of both types... they all worked after being demolded.... NOW its getting closer to actually having to use them and I tested them again. Quite a few don't work either or colours or nothing..... So the only possible expalation I'm thinking that as the resin "matures and cures" fully it shrinks by only one modicum and thats enough to tear the soldered joints inside.
I had to prove my theory so using a 1mm ball in my dental drill I excavated the back of a couple to expose the soldered joints and found that precisley is what happened a touch with the soldering iron with a fine tip and all is A ok... Then nurse filled the holes with plasti bond....
Certainly a problem I did not envisage.... I may have to rethink this... Curiously its only the signals themselves, the other encapsulated components are not affected.... probably something to do with the fact that the polyester resin I used does not actually stick to the LED casings

 

[tramcar trev]

Only problem with the encapsulation resin is that it is epoxy and too viscous ( and does not "wet" the silicone) to get into the detail in my moulds. I did try the stuff that comes in the single dose pack.....

 

[bobg]

Only problem with the encapsulation resin is that it is epoxy and too viscous ( and does not "wet" the silicone) to get into the detail in my moulds. I did try the stuff that comes in the single dose pack.....

Trev, how about coating the wire/joint with something the resin doesn't stick to. I dunno, perhaps a wipe with a bit of Vasaline?

 

[ntpntpntp]

Perhaps a bit of heat-shrink sleeve around the solder joints would be enough to protect them from the direct strain?

 

[ntpntpntp]

Must admit I'm quite surprised that the small amount of resin in these signal mouldings would shrink enough to break a solder joint. If this is truly the cause then the solution has to be something to keep the resin away from the joints, be it sleeving, vasoline, insulation tape or whatever else folk can think of.

How about using a small mount of proper non-shrink potting compound only around the joints, then encase everything in the moulding resin?

Brilliant looking signal heads btw!

 

[nicebutdim]

I use a hot glue gun. Cheap and works a treat.

 

[tramcar trev]

Great ideas... I'll use a drop of liquid masking tape, let that set then pot up any new ones